Nitrification inhibitor (NI) and urease inhibitor (UI) with fertilizer have the potential to reduce nitrogen (N) loss as well as improve grain yields. Urea–ammonium nitrate (UAN) solution as liquid fertilizer is superior to conventional solid nitrogen (N) fertilizer in terms of fertilizer efficiency, energy savings, environmental pollution reduction and economic benefits. However, comprehensive assessments of UAN with inhibitors from an environmental and agronomy perspective, including insights into the mechanisms of UAN with inhibitors, are lacking. In a field trial, three single-inhibitor and two double-inhibitor (DI) treatments were set to quantify the grain yield, the N losses and the N recovery efficiency of maize treated with urea supplemented with dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP) and N-(n-buty_l) thiophosphoric triamide (NBPT). Compared with the UAN treatment, the supply of urease inhibitors reduced NH₃ emission by 13.0% but increased N₂O emission by 13.0%. The supply of nitrification inhibitors delayed the conversion of ammonium N to nitrate N and improved NH₃ emission by 23.5–28.7%, but reduced N₂O emission by 31.4% and significantly increased the maize yield by 21.3%. The combined use of NBPT and DCD were not compatible in UAN and cannot achieve the maximum potential for optimizing yields and reducing nitrogen losses. Considering the grain yield, the N use efficiency and the N losses, the combined use of NBPT and DMPP in maize production system significantly improved the grain yield and N use efficiency, as well as reduced N losses.

Poor grain filling severely reduces rice yield. Fertilizers play a vital role in regulating grain filling, especially nitrogen (N) and potassium (K). In this field study we aimed to investigate the interactive effects of N and K on the asynchronous filling properties of superior and inferior spikelets of japonica rice. We looked at grain filling under three N rates (0, 90, and 180 kg N ha⁻¹) and three K rates (0, 60, and 120 kg K₂O ha⁻¹) during 2020 and 2021. Across two years, the results showed that the combined use of N and K on superior and inferior spikelets significantly increased their weight by 1.29 mg and 2.31 mg, their maximum grain filling rate by 0.24 mg d⁻¹ and 0.07 mg d⁻¹, and their average grain filling rate by 0.21 mg d⁻¹ and 0.06 mg d⁻¹, respectively, in comparison with the control (N0K0) treatment. Likewise, K supply increased the average contribution rate of superior and inferior spikelets to yield by 9.1% and 10.0%, respectively. Correlation analysis showed that the grain filling rate of superior and inferior spikelets was an important factor in determining the spikelet weight, whereas the grain filling time was not. We also found that the 1,000-grain weight mainly increased after increasing the spikelets’ maximum grain filling rate and average grain filling rate. Collectively, these results illustrate that the combined use of N and K can optimize the asynchronous filling of superior and inferior spikelets and, in particular, enhance inferior spikelet weight with higher rice yield.

Straw returning enhances soil fertility and increases corn yield, but the impact on soil fertility varies with different incorporation methods. To explore the optimal straw-returning method, this study, based on a long-term field experiment, investigated the following different corn-straw-returning methods: deep plowing and straw returning (B), rotary tillage and straw returning (RT), crushing and mixing straw returning (TM), pulverized cover straw returning (C), high-stubble-retention straw returning (LHS), strip cover (S), and flat no-tillage without straw returning (CK). High-throughput sequencing technology was employed to analyze the soil bacterial community composition and structural changes under different straw-returning methods. The study further explored the relationships between the soil bacterial community and nutrient content. The results indicated that different straw-returning methods altered the composition and structure of the soil bacterial community. The TM treatment significantly increased the richness and diversity of the soil bacterial communities. Shredding and covering (C and TM) effectively improved the soil nutrient content and bacterial community structure. In the C treatment, the abundance of Blastococcus, Nocardioides, and Microvirga increased the most, by 241.02%, 77.79%, and 355.08%, respectively, compared with CK. In the TM treatment, Pseudarthrobacter showed the highest abundance, increasing by 343.30%. The genes involved in soil carbon hydrolysis (pulA), nitrification (hao), organic nitrogen degradation and synthesis (gudB), and the nitrogen limitation response (glnR) significantly decreased by 56.21%, 78.75%, 66.46%, and 67.40%, respectively, in the C treatment. The genes involved in soil carbon hydrolysis (IMA), carbon fixation (pccB-A), methane metabolism (moxF), nitrate reduction in soil (nirD), organic nitrogen degradation and synthesis (gdh, ureAB, ureE), and phosphate absorption (glpT) significantly increased by 93.37%, 92.68%, 95.00%, 23.42%, 35.40%, 114.21%, 59.14%, and 75.86%, respectively, in the C treatment. The nitrate reduction gene (nrfA) significantly increased by 80.27% in the TM treatment. Therefore, we concluded that straw primarily stimulates the activity of bacterial communities and regulates the bacterial community by changing the relative abundance of the soil microorganisms and functional genes, thereby improving the soil nutrient content. This study considered pulverized cover straw returning and crushing and mixing straw returning to be the most reasonable methods.